One popular idea to explain the current obesity epidemic
proposes that our hunter-gatherer ancestors had a fat-storing adaptation, which allowed
them to survive frequent famines. Today, with our overabundance of food, this
adaptation is causing us to get fat. There's just one problem with this idea
— research now shows that hunter-gatherer societies aren't necessarily
prone to food shortages.

The Thrifty Genotype
Hypothesis

The notion that hunter-gatherer societies experience
frequent periods of food shortage and even famines is pervasive across a number
of scientific fields, including paleoanthropology and evolutionary psychology. This
concept has even helped shape a variety of different theoretical models in
everything from biology to economics — the "thrifty genotype
hypothesis" is, perhaps, one of the most notable.

The thrifty genotype hypothesis (and other related theories)
stems from the idea that our hunter-gatherer ancestors had an evolutionary adaption
that allowed them to survive the frequent famines they must have faced. This
adaptation still persists today, according to the hypothesis.

"If it were true, it would mean that some or all people
have an extreme genetic predisposition to convert calories more efficiently to
fat," Colette Berbesque, an evolutionary anthropologist at the University
of Roehampton in the UK, told io9. "We've gotten so good at turning
calories into fat for later use that we are all just getting obese because we don't
have those lean times anymore."

Initially, scientists thought they had found evidence for
the hypothesis when they looked at the subsistence practices of Samoans, Pima
Native Americans and the Yanomami. People of these societies, they found, quickly
experienced rising levels of obesity when they ditched their traditional diets.
But it turned out that the groups had actually been involved in non-intensive
agriculture — such as horticulture combined with hunting — for a long time, and that it was the "westernization" of their diets that led to
their weight gain.

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A couple of other studies compared the rates of famine and
food shortages among people utilizing different types of subsistence, including
agriculturalists, horticulturalists, hunter-gatherers and pastoralists. The
research showed that hunter-gatherers experienced famines at about the same
rate as other people. But when Berbesque took a closer look, she found that the
studies didn't take into account different habitats. Half of the
hunter-gatherer societies that researchers have data on live in arctic or
subarctic regions, where very few agriculturalists live. What's more, it's
impossible to tell an evolutionary story with just this sample, because many hunter-gatherers
of the past lived in warm areas, Berbesque said.

So Berbesque and her colleagues decided to take another look
at hunter-gatherer societies to see if they really do suffer from more famines
than other people.

Hunter-Gatherers Vs.
Agriculturalists

For their study, the team used the so-called standard
cross-cultural sample, which is a massive database containing information on
186 societies across the globe, including 36 hunter-gatherer societies. The
database, which is primarily a sample of preindustrial societies, is coded with
thousands of different variables, including famine, diseases, marital patterns,
incidences of conflict, location, rainfall, temperature, plant productivity and
many others.

The researchers compared hunter-gatherer societies — defined
as non-horseback hunting societies that obtain less than 10% of their
nutrition from farmed goods or animal husbandry, and engage in minimal trade
— with agriculturalists, based on eight different famine-related variables, such
as occurrence of short-term starvation, persistence of famine and recurrence of
famine. To make sure the habitats were similar, they only looked at cultures
that lived in regions with an effective temperature, which is the average
temperature of the warmest and coldest months, of at least 13 degrees Celsius
(55.4 degrees Fahrenheit). The societies they included also had similar
"net primary productivity," which has to do with the amount of new
plant growth each year, Berbesque explained.

"We wanted to only statistically compare hunter-gatherers
with agriculturalists that had similar habitats," Berbesque said.
"Once we did that, we found that hunter-gatherers had significantly less
bouts of famine."

In particular, hunter-gatherers had less
famine than the agriculturalists across five of the eight variables, including
occurrence of famine, severity of famine and persistence of famine.
Interestingly, the hunter-gatherer societies also had lower scores for the
"contingency of famine" variable. That is, the agriculturalists were
more prepared for famines, which, depending on how you look at it, could mean
they had to deal with food shortages more often.

Berbesque thinks there are a few reasons why contemporary
hunter-gatherer societies were less prone to famines than agriculturalists. For
one, they weren't tied to the land, so if they experienced a major change in
their food source, they could just pick up and move to a better location.
Another reason could be that they just used their land differently. It's
sometimes said that preindustrial hunter-gatherers occupied marginalized
habitats that weren't as productive as agriculturalists' habitats, but this
idea comes from a farmer's point of view — while the land may not have been
good for farming, it was still fine for other modes of subsistence.

Though the literature is rife with references to the
"feast and famine" lifestyle of ancient hunter-gatherers, the study
suggests it wasn't like that at all — a finding with important
consequences.

"I think that the thrifty genotype, as an evolutionary
story in explaining the western obesity epidemic, is misplaced," Berbesque
said. Additionally, some people today adhere to diets that recommend periodic
fasting, in an attempt to mirror the diets of our lean ancestors. But the
study, as well Berbesque's own observations of modern hunter-gatherer
societies, shows the idea behind this practice may be unfounded.